int numRows = 5;
int numCols = 5;

#define period (2.0)
#define halfperiod (period * 0.5)
#define dt (mod(iTime, period))
#define dth (mod(iTime, halfperiod))

#define moveFlip (int(mod(iTime, period * 2.0) > period))
#define moveRows (int(mod(iTime, period) > halfperiod))
#define moveEvens (int(mod(iTime, period) > halfperiod))



void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    int move_evens = moveEvens;
	if (moveFlip > 0)
	{
		move_evens = 1 - moveEvens;
	}

	float dx = iResolution.x / float(numRows);
	float dy = iResolution.y / float(numCols);

	float x = fragCoord.x;
	float y = fragCoord.y;

	x *= iResolution.x/iResolution.y;


	int rowx = int(x / dx);
	int rowy = int(y / dy);

	int xeven = int(mod(float(rowx), 2.0));
	int yeven = int(mod(float(rowy), 2.0));

	float t = dth / halfperiod;

	float dtx = dx * t * 2.0;
	float dty = dy * t * 2.0;

	if (moveEvens == 1)
	{
		if (moveRows == 1 && xeven == 1)
		{
			y = y + dty;
			rowy = int(y / dy);
		}
		else if (moveRows == 0 && yeven == 0)
		{
			x = x + dtx;
			rowx = int(x / dx);
		}
	}
	else
	{
		if (moveRows == 1 && xeven == 0)
		{
			y = y + dty;
			rowy = int(y / dy);
		}
		else if (moveRows == 0 && yeven == 1)
		{
			x = x + dtx;
			rowx = int(x / dx);
		}
	}

	xeven = int(mod(float(rowx), 2.0));
	yeven = int(mod(float(rowy), 2.0));

	if (xeven == yeven)
	{
// 		vec4 c = texture(iChannel0, fragCoord.xy / iResolution.xy);
//
// 		if (c.x == 0.0 && c.y == 0.0 && c.z == 0.0)
// 		{
// 			c = vec4(1.0, 1.0, 1.0, 1.0);
// 		}
//
// 		fragColor = c;
        fragColor = vec4(1.0, 1.0, 1.0, 1.0);
	}
	else
	{
// 		vec4 c = texture(iChannel1, fragCoord.xy / iResolution.xy);
// 		fragColor = c;
        fragColor = vec4(0.0, 0.0, 0.0, 1.0);
	}
}